Product Survey: Memory Cards

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The sensors in digital cameras are getting bigger and bigger, and so are the size of files captured onto memory cards, but the memory you use can often be as important as the camera itself--especially when it comes to how long it takes to move your photos around.

Pierre-Jean Alzieu
Updated: November 17, 2008

Our Tests

The test procedure is similar to the one used for memory card readers. We test the different cards on a Transcend Multi-Card Reader with three types of files:

• several small spreadsheets: 100 KB each
• large files: 256 MB each
• a series of photo files from 2 to 5 MB

We note the time of transfer in writing and in reading in order to give a value expressed in MB/s.

To this we add a practical test with a 10 Megapixel digital SLR, either the Nikon D40x or the Nikon D60. We set the camera to burst mode and first take five shots, and then another thirty, noting whether or not writing to the memory card slows down the burst.

These days, it's difficult to leave the house with just a single 2 GB SD card. Now that larger SDHC cards are available in sizes up to 16 GB, which ones are the fastest? And what about the new ''Class'' system for identifying the data transfer rate of different cards?

SDHC, or High Capacity SD cards, are ideal for owners of digital cameras with 10 Megapixel or bigger sensors.

With a single JPEG image weighing in at up 5 MB, and JPEG+RAW files approaching 20 MB, it's very easy to fill a 2 GB SD card.

Bigger cards, new standards

The SDHC standard currently allows for cards of up to 16 GB, with the promise of 32 GB cards in the future.

Compared to the classic SD, the SDHC also adds a new system for classifying cards according to how fast they are at transferring data. No more X's -- say 'hello' to the three new "Classes": 2, 4 and 6.

They serve in certifying minimum speeds of 2, 4 and 6 MB/s, respectively.

In practice, these classes are well-respected by manufacturers, although there is sometimes a tendancy to over-estimate speeds.

However, as usual, a few products stand out from the others to the point that today it seems necessary to enlarge the class system perhaps as far as Class 14 or even further.

Some cards in our tests reach up to 20 MB/s, but are still counted as 'Class 6' because they reach at least 6 MB/s.

In fact, while cards generally surpass their specification speeds by several MB/s, there are some whose writing speeds really outpace the competition.

For example, the Class 6 PNY Optima SDHC 4 GB offers a maximum of 10.33 MB/s while the overachiever at the moment is the ATP ProMax 4 GB, also a Class 6, with no less than 15.57 MB/s when writing large files.

SD and SDHC: not the same thing!

Unless your memory card reader specifically offers support for SDHC cards, it may not be able to read them.

Both types of card (SD and SDHC) look the same, but only certain readers are capable of accessing the newer SDHC cards.

Remember that SD cards are only ever 2 GB or smaller, so if you have a card at 4 GB or larger, then it has to be an SDHC card and you will need an SDHC-compatible card reader.